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Abstract

The method of isotope substitution in neutron diffraction was used to measure the structure of liquid ZnCl2 at 332(5) degrees C and glassy ZnCl2 at 25(1) degrees C. The partial structure factors were obtained from the measured diffraction patterns by using the method of singular value decomposition and by using the reverse Monte Carlo procedure. The partial structure factors reproduce the diffraction patterns measured by high-energy x-ray diffraction once a correction for the resolution function of the neutron diffractometer has been made. The results show that the predominant structural motif in both phases is the corner sharing ZnCl4 tetrahedron and that there is a small number of edge-sharing configurations, these being more abundant in the liquid. The tetrahedra organize on an intermediate length scale to give a first sharp diffraction peak in the measured diffraction patterns at a scattering vector k(FSDP) similar or equal to 1 angstrom(-1) that is most prominent for the Zn-Zn correlations. The results support the notion that the relative fragility of tetrahedral glass forming MX2 liquids is related to the occurrence of edge-sharing units.